Various types of dispensers are used in many industries for placing liquids, such as adhesives, conformal coating materials, solder paste, solder flux, and other similar materials, onto substrates during an assembly process. One type of liquid dispenser is a syringe-type dispenser having a dispenser body defining a barrel reservoir for holding a supply of liquid material to be dispensed. A dispensing tip is coupled to the syringe at one end, and is in fluid communication with the reservoir. A piston disposed in the reservoir is movable therein to pressurize the liquid in the reservoir and thereby dispense a small amount of liquid from the dispensing tip and onto a substrate.
Many industrial applications require that the liquid be dispensed in very precise volumes and at precise locations. To this end, liquid dispensers include actuators for moving the piston within the reservoir in a controllable and predictable manner. For instance, pneumatic actuators are known in the art and use compressed gas, such as air, applied to the piston to move the piston and dispense liquid from the dispenser. Those skilled in the art will recognize that other types of actuators, such as linear actuators, may be used to control movement of the piston within the reservoir. In other applications where precise dispensing is not required, the piston may be moved through manual processes.
Often times, pneumatic actuators are prone to a phenomenon known as “piston bounce.” Piston bounce generally refers to the accumulation of entrapped gas between the piston and the liquid. Thus, when the piston is actuated by the compressed gas, the piston effectively “bounces” on the entrapped gas before contacting the liquid within the dispenser. The effects of piston bounce decrease performance of the liquid dispenser and may range from minor inconsistencies in the dispensed liquid to a tunneling of the liquid within the liquid dispenser that may require disposal of the remaining liquid.
Traditional solutions for improving performance of such liquid dispensers often attempt to balance piston bounce with liquid waste. Specifically, the piston may include or at least partially define passages such as vents, micro-vents, flow channels, or increased clearances to direct entrapped gas from the liquid, beyond the piston, and into an ambient environment. While relatively effective at reducing piston bounce, these passages also tend to release liquid that, in turn, creates significant waste.
There is a need for a liquid dispensing syringe and method for reducing piston bounce that effectively dispenses liquid while addressing issues such as those discussed above.